He looked genuinely concerned, and, calling to one of the men, said: “Here, Pat, take these two boys to the doctor at once, and tell him they can’t whistle.”
Pat grinned from ear to ear as we made for the ladder and began climbing like mad. I thought we should never reach the lock. A hundred feet up was three times as much as a hundred feet down. Try running up to the ninth floor of a building, and then imagine how much harder it would be to make that same ascent up a vertical ladder. What if the paralysis spread to our arms and legs before we got to the top! We were pretty well fagged before we reached the lock and scrambled through the lattice, but the rich oxygen we took in with every breath sustained us wonderfully. Pat was not far behind us. He shouted to us to get down out of the way of the trap-door, then he gave the signal, and presently the door fell open.
We dragged ourselves into the lock and the door closed behind us; then we waited an interminable time for the compressed air to be let out. The chamber filled with fog as the pressure was reduced, and, after a time, the upper door clanged open, and we jumped out into the sunshine.
A shift of sand-hogs gathered around the door of the doctor’s shack as we were ushered in.
“Docther,’ said Pat, “these bhoys is afflicted with serious symptims. Their whistlin’ orgins is paralyzed.”
“Most distressing, most distressing,” replied the doctor. “You will have to get them a tin whistle, Pat.’ The guffaws of laughter that greeted this prescription were disconcerting, to say the least. We were completely taken in. How should we know that it is very difficult to whistle in air as dense as that in a caisson, and that only by considerable practice can one acquire the art of making “lip music” under pressure? However, there was nothing to do but to laugh with the rest, and make the best of the joke. The doctor made us stay in his office for a half-hour or so, to keep us from becoming chilled, and made up for the prank he had played upon us by recounting some very curious adven- tures he had had. Presently Mr. Squires came in, and we had to go over the whole story again.
THE WORKING CHAMBER:OF A WOODEN CAISSON.
“It was one on us, all right,” said Will, with a forced laugh; “but you sent us out before we had seen half there was to see. You will have to answer questions now. What do you do when the caisson is sunk all the way down to rock?”
“We blast out a good footing if the rock is tilted.”
“What! You blast rock down in that small chamber!”
“Oh, yes, the sand-hogs all get out of the chamber when the charge is set off. We have a trap-door at the bottom of the shaft. The men all climb into the shaft and pull up the trap-door, then the gang boss sets off the charges with electricity.”
“But after you have finished blasting, what then?”
“Oh, then we just fill in with concrete. The concrete is laid round the cutting edges first. The filling then proceeds toward the center. Then we work up the shaft, filling up the hole behind us until the entire pier is built up solid. What next?” asked Mr. Squires.
“I can’t think of anything more; can you, Will?”
“No, not without going in again,” he replied.
“You can go down with Danny Roach in one of the narrow coffer-dam caissons, if you like,” he answered. “We find it necessary to build a solid wall all the way down to rock on two sides of the building, because we expect to have a pretty deep cellar, and the adjacent buildings were built on floating foundations. Not many years ago, foundations used to be made that way. Piles were driven into the mud and sand as close to one another as possible, and then upon them was built a grillage of iron rails, that is, the rails were piled in tiers that crisscrossed one above the other, and upon this grillage the columns of the building were supported. That form of foundation is pretty good until some one digs a deep hole near by, then, under the weight of the building, the quicksand oozes into this hole, and the building settles badly, sometimes dangerously.
In Chicago, most of the buildings are supported on floating foundations, because the sand is so deep that it is impossible to get down to rock. A man can’t work at much more than 110 feet below water-level, because the pressure would be over 47 pounds per square inch. Some Chicago
